Independent solution

How to solve this Conditional Probability question

Setup

Setup

Conditioning on treatment restricts the denominator to treated policyholders from both heart-rate categories.

ntreated=60+28=88n_{\mathrm{treated}}=60+28=88

Model

Model

Within that restricted group, the favorable count is the number from the low-or-normal category.

Pr(LS)=n(LS)n(S)\Pr(L\mid S)=\frac{n(L\cap S)}{n(S)}
Pr(LS)=2860+28\Pr(L\mid S)=\frac{28}{60+28}

Compute

Compute

Reduce the count ratio and convert it to a decimal.

2888=722=0.3181818182\frac{28}{88}=\frac7{22}=0.3181818182

Answer

Answer

Approximately 31.8% of the treated subgroup belongs to the requested category.

0.318(C)\boxed{0.318\quad\text{(C)}}